JPS644315Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control device for a DC motor having a current limiting function.

Now, a DC motor speed control device called an electronic governor compares the back electromotive force generated in the drive coil in proportion to the rotational speed of the DC motor with a reference voltage, and uses the difference voltage between the two for control purposes. Controls the transistor to maintain a constant rotational speed of the DC motor.

By the way, a circuit configuration suitable for implementing such an electronic governor into a semiconductor integrated circuit has already been proposed in Japanese Patent Application No. 52-80817.

FIG. 1 shows an example of the circuit configuration of the electronic governor.

In FIG. 1, a transistor 5 whose collector is connected to a power supply terminal 3 through a resistor 2 and whose emitter is grounded through a resistor 4, and a transistor 5 whose collector is commonly connected and whose collector is connected to a power supply terminal 3 through a controlled DC motor 1 are shown. DC motor drive transistors 9, 10, and 11, each emitter of which is grounded via resistors 6, 7, and 8 set to the same value, have their bases commonly connected to form a current mirror. ing.

Further, one input terminal is connected to the other end of a reference voltage source 12 whose one end is connected to the collector of the transistor 5, and the other input terminal is connected to a common connection point of the collectors of the transistors 9, 10, and 11, a comparator 13 whose output terminal is connected to the base common connection point of the transistor 5 and the transistors 9, 10, and 11; a constant current source 14 for driving the reference voltage source 12 with a constant current; A resistor 15 is provided between the collector and the collector common connection point of the transistors 9, 10, and 11.

In the DC motor speed control device having the above configuration, a control operation is performed to keep the rotational speed of the DC motor 1 constant by comparing the reference voltage V _ref of the reference voltage source 12 and the back electromotive force Ea of the DC motor 1. is executed.

For example, when the rotational speed of the DC motor 1 decreases due to the influence of external load torque, etc., the following circuit operation is performed to control the rotational speed to a constant value. That is, as the rotational speed of the DC motor 1 decreases, the back electromotive force Ea decreases, and the DC motor drive transistors 9, 10, 1
The potential at the collector common connection point of No. 1 becomes high. Therefore, one input voltage of the comparator 13 becomes high, and the comparator 13 is connected to the transistors 5, 9, 10, 11.
It works in the direction of increasing the amount of base current supplied to. Therefore, the DC motor driving transistors 9, 1
0 and 11 are about to increase, the armature current Ia increases, and control is performed to increase the rotational speed of the DC motor multiplier 1.

In the DC motor speed control device shown in Fig. 1,
The back electromotive force of DC motor 1 is Ea, the armature current is Ia,
The internal resistance is Ra, the reference voltage is V _ref , the constant current of the constant current source is Ir, the current ratio between transistor 5 and transistors 9, 10, and 11 forming the current mirror is K, and the resistance value of resistor 2 is R _T and the resistance value of the resistor 15 is R _S , the rotational speed N of the DC motor 1 is N=1/Ka [V _ref {1+R _T /R _S (1+1/K)} +Ia (R _T /K-Ra ) + R _T Ir] …(1). Note that Ka is the power generation constant of the DC motor 1.

Now, the internal resistance Ra of the DC motor 1
Correspondingly, if the resistance value R _T of resistor 2 is set to R _T =KRa …(2), then equation (1) becomes N=1/Ka [V _ref {1+R _T /R _S (1+1 /K)}+R _T Ir] (3) Therefore, the DC motor 1 is not affected by the armature current Ia, that is, the load torque, and has a constant rotation speed.

By the way, in a conventional DC motor speed control device having a circuit configuration as shown in FIG.
If the DC motor 1 is in an overload state such as a locked state for a long time, there is a risk that excessive current will flow to the DC motor 1 and the speed control device, causing destruction or excessive heat generation, which may cause smoke or fire. Ta.

That is, when the DC motor 1 is in the locked state, the back electromotive force Ea becomes zero, and the potential at the common connection point of the collectors of the DC motor drive transistors 9, 10, and 11 becomes high. Therefore, one input voltage of the comparator 13 increases, and the comparator 13 increases the amount of base current supplied to the transistors 5, 9, 10, 11, and the DC motor drive transistors 9,
10 and 11 cause the maximum drive current to flow.
If such an overload state such as a lock state continues for a long time, the DC motor 1 and the driving transistors 9, 10, 11 will overheat due to the excessive current, which may cause smoke or fire. I was thinking of triggering it.

The present invention solves this problem by providing a current limiting circuit that uses the resistor 2 or the terminal voltage of the resistor component constituting the resistor 2 as the detection voltage, and uses the output voltage to control the DC motor driving transistors 9 and 1.
The purpose is to solve this problem by limiting the drive current of 0 and 11.

An embodiment of the present invention will be described below with reference to FIG. 2. Elements similar to those shown in FIG. 1 will be designated by the same reference numbers, and their explanation will be omitted here.

Current limiting circuit 16 in the embodiment of FIG.
The circuit configuration of is explained below.

First, the resistor 2 in FIG. 1 is divided into a series circuit of a resistor 17 and a resistor 18. Here, the sum of the values of the resistor 17 and the resistor 18 is made equal to the value R _T of the resistor 2 in FIG. 1. and,
The base of a PNP transistor 19 is connected to the connection point between the resistor 17 and the resistor 18, the emitter of the transistor 19 is connected to the power supply terminal 3 to which the resistor 17 is connected, and the collector is connected to the base of the NPN transistor 20. There is. Further, the emitter of the transistor 20 is grounded, and the collector is connected to the transistor 5, the driving transistor 9,
It is connected to the base common connection point of Nos. 10 and 11. Furthermore, a resistor 21 is connected between the base and emitter of the transistor 20.

Now, in this circuit configuration, if the DC motor enters an overload state such as a lock state and the armature current Ia increases, Ia/K
Since the current flows through the resistor 2, the terminal voltage of the resistor 17, which is the resistance component of the resistor 2, increases. When the terminal voltage becomes sufficient to turn on the transistor 19, the transistor 1 is turned on.
Collector current flows through transistor 9, then transistor 2
0 is turned on, and the base currents of the transistor 5 and the driving transistors 9, 10, 11 are diverted as the collector current of the transistor 20, so that the driving transistors 9, 10, 11 are turned on. This limits the drive current and prevents excessive current from flowing.

As described above, according to the present invention, in this type of DC motor speed control device, even if the DC motor remains in an overload state such as a locked state for a long time, an excessive current flows through the DC motor and the drive transistor. Smoke emitted due to destruction or excessive heat generation.
It is possible to avoid ignition, etc., and can be highly effective as a safety measure.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a conventional DC motor speed control device, and FIG. 2 is an electric circuit diagram of a DC motor speed control device according to an embodiment of the present invention. 1... DC motor, 2... First resistor, 3...
Power supply terminal, 5...first transistor, 9, 1
0, 11... Second transistor, 12... Reference voltage source, 13... Comparator, 16... Current limiting circuit.

Claims (1)

[Claims for Utility Model Registration] A first transistor whose collector is connected to a power supply terminal via a first resistor and whose emitter is grounded; whose base is commonly connected to the base of the first transistor; a second transistor connected to the power supply terminal via a DC motor and whose emitter is grounded, and a voltage obtained by subtracting the sum of the voltage drop of the first resistor and the voltage of the reference voltage source from the voltage of the power supply terminal; and a voltage obtained by subtracting the voltage applied to the DC motor from the voltage of the power supply terminal, and a comparator that returns the output to a common connection point of the bases of the first and second transistors, means for controlling the rotational speed of the DC motor by operating so that the current flowing through the DC motor and the current flowing through the first resistor are always proportional; and the first resistor or the first resistor. a third transistor that detects a current proportional to the current flowing through the DC motor as a voltage drop of a resistive component forming a part of the DC motor, and the voltage drop is applied between the base and emitter of the third transistor; a fourth transistor connected to the collector of the transistor, the emitter of which is grounded, and the collector of which is connected to a common connection point of the bases of the first and second transistors, the voltage drop being connected to the base of the third transistor; - Speed control of a motor comprising a current limiting circuit that turns the first and second transistors off by turning on the third and fourth transistors when an emitter-to-emitter threshold voltage is exceeded. Device.